Vulcanization of halogenated butyl rubber polymers



United States Patent VULCANIZATION 0F HALOGENATED BUTYL RUBBER POLYMERSRichard H. Dudley, Cranford, NJ., assignor to Es so Research andEngineering Company, a corporation of Delaware No Drawing. Originalapplication Aug. 26, 1960, Ser. No. 52,021. Divided and this applicationMar. 4, 1963, -Ser. No. 262,381

1 Claim. (Cl. 26078.4)

The present invention relates to improved vulcanizable compositions ofhalogenated copolymers of isoolefins and multiolefins. Moreparticularly, it deals with curing halogenated butyl rubber at anaccelerated rate to give a vulcanizate of improved physical and dynamicproperties.

This is a divisional application of Serial No. 52,021, filed August 26,1960.

Copolymers of the above general class, particularly where the copolymerscontain about 85 to 99.5 wt. percent .of a C to C isoolefin, e.g.,isobutylene, with about 16 to 0.5 wt. percent of a multiolefin of about4 to 14 carbon atoms, e.g., myrcene, isoprene, butadiene,3-methyl-butene-l, etc. are well known in the literature as butylrubber. For example, see Synthetic Rubber by G. S. Whitby, and US.Patent 2,356,128 among many others. Polymerization is generally carriedout at low temperatures, i.e. 50 to l65 C. in the presence of Friedel-Crafts catalyst such as aluminum chloride dissolved in a lower alkylhalide. Butyl has viscosity average molecular weight of 200,000 to1,500,000 and mole percent unsaturation of about 0.1 to 30. Halogenatedbutyl rubber-type copolymers are produced by halogenating butyl rubberin a manner which does not substantially degrade its molecular Weightbut, however, gives a rubbery product of substantially differentproperties than the unhalogenated material. Butyl rubber may behalogenated at temperatures of -50 200 C., preferably 0 to 100 C., andat pressures of 0.5 to 900 p.s.i.a with suitable halogenating agentssuch as gaseous chlorine, liquid bromine, iodine monochloride, etc.Halogenation may be accomplished in various ways. For example, thehalogenation agent, e.g., chlorine, may be added to a solution of thecopolymer in a suitable inert liquid organic solvent. The resultinghalogenated polymer may be recovered by precipitation with a non-solventat about 0 to 180 C., spray drying, or by flashing off the hydrocarbonsolvent by injection into a hot water bath.

Preferably, the degree of halogenation, is carefully regulated so thatthe halogenated copolymer contains at least 0.5 wt. percent of combinedhalogen but not more than about one atom of combined fluorine orchlorine per double bond in the polymer, nor more than three atoms ofcombined bromine or iodine per double bond. The brominated andchlorinated copolymers are preferred. A more detailed description of theformation of chlorinated butyl rubber may be had by referring tocoassigned Serial No. 512,182, filed May 31, 1955, now US. No.2,944,578, patented July 12, 1960.

The halogenated copolymer has a viscosity average molecular weight ofabout 100,000 to 2,000,000 and a mole percent unsaturation of between0.1 to 20, preferaably less than 10. As hereinafter employed in thespecification, the term halogenated butyl rubber denotes theabove-described halogenated copolymers of a major portion of a C to Cisoolefin and a minor portion of a C to C multiolefin.

Although halogenated butyl rubber can be used in the manufacture ofnumerous articles, because of its relatively low degree of unsaturationand small percentage of halogen, e.g., 0.5 to 3%, it does not cure asquickly as other more highly unsaturated rubbery polymers. Materialswhich will accelerate the cure of natural rubber or butadieue-styrenerubber, such as guanidines, may not increase the cure rate ofhalogenated butyl rubber. Thus, there exists a need for a system wherebyhalogenated butyl rubber may be more rapidly cured to give a vulcanizateof good physical properties. Such a cure system is particularly desiredin applications of halogenated butyl rubber such as tubeless tires, shoesoles, wire coatings, conveyor belting and extrusion and molding ofitems such as automobile motor mounts.

In accordance with the present invention, halogenated butyl rubber maybe rapidly cured to give a vulcanizate having good physical properties.More particularly, it has now been discovered that excellent cures. areobtained within a short period of time by curing halogenated butylrubber inthe presence of certain compounds which are known in the art asretarders for high unsaturation rubbers, e.g. natural rubber,butadiene-styrene, etc. More particularly, halogenated butyl rubber iscured in the presence of an accelerating quantity, e.g., 0.1 to 15,preferably 0.5 to 10, parts by weight per hundred of rubber of a memberof the group consisting of wood rosins (unhydrogenated, hydrogenated,and esten'fied), benzoic acid, salicylic acid and maleic anhydride.

This is indeed a surprising result. It would be expected that theseknown high unsaturation rubber retarders, such as wood rosin, benzoicacid, salicylic acid, maleic anhydride, etc. (see India Rubber WorldHandbook of Compounding Ingredients, Edition II, Conway Printing Co.,New York, 1947), would retard, to even a greater degree, the cure rateof a less unsaturated rubber such as halogenated butyl rubber. However,exactly the converse has been discovered,

The unexpected nature of the action of the above specific materials isemphasized by the fact that very closely related compounds such assuccinic acid, fumaric acid (known retarders) and phthalic anhydridewill not accelerate the cure of halogenated butyl rubber. The inabilityof phthalic anhydride to accelerate the cure of halogenated butyl rubberis particularly noteworthy. Phthalic anhydride is a known acceleratorfor chloroprene rubber (neoprene). Thus its inability to enhance thecure rate of low unsaturation, low halogen content, halogenated butylrubber clearly indicates the latters basic dissimilarity to highunsaturation, high chlorine content neoprene rubbers. This is furtherdemonstrated by the fact that curing agents for neoprene rubbers, suchas magnesium dioxide, will not cure halogenated butyl copolymers.

The compositions of the present invention may be cured under a broadrange of temperatures, e.g. 200 to Patented June 7, 1966 may contain 1to 20% of a metal oxide, such as zinc oxide, and/or minor proportions,e.g. 0.1 to 15 wt. percent of sulfur, tetramethyl thiuram disulfide,benzothiazyl disulfide or mercaptobenzothiazole.

Vulcanization recipes prepared in accordance with the present inventionmay contain the various additional materials such as carbon black,mineral fillers, pigments, anti-oxidants, extender oils, etc. Ifdesired, blends of halogenated butyl rubber and other rubbery polymers,e.g. natural rubber, butadiene-styrene rubber, etc. may be covulcanized.

TABLE I Base Recipe, Parts by Weight:

Halogenated Butyl Rubber A- lgO MT Black. EP0 Black 20 Process 0 15 ZincOxid 5 Sample- Control (a) (b) (c) (d) (e) (D Activator Type SulfurStey- Stay- Wood Benzoic Succinic belite belite Rosin Acid Acid ResinEster Activator Cone, phr 0 1 5 5 5 1 1 Tensile Strength, p.s.i.Cure at1,060 520 1,080 450 1,150 320 1, 260 900 160 160 170 1, 180 1,100 1, 2201, 020 290 270 380 1, 070 1, 050 1, 200 1, 050 540 1, 090 1,060 1,100 1,070 1, 200 980 880 1, 100 1, 050 1, 060 1, 050 1, 180 1, 190 1,050 90mins 1, 040 1,120 1, 040 1,080 1,120 1,150 1, 050 Modulus at 300%,psi-Cure at ruins 500 220 650 200 mins 570 370 700 430 100 1111115-- 110100 500 500 700 500 160 mins 150 120 470 500 670 570 200 1111115 550 500500 550 700 600 540 nuns 620 620 510 550 670 640 590 90 mins 670 750 580580 750 680 700 Elongation at Break, percent- Cure at 287 F.:

15 mins 650 550 590 600 20 B11115 610 540 620 550 880 25 1111115.- 960940 640 540 590 530 780 30 mins. 740 770 620 540 030 510 680 45 mins 470500 610 520 610 470 460 60 mp1s. 460 470 570 490 620 470 450 90 1111113450 440 570 500 580 480 420 Time to Reach Optimum Tensile,

Mins 45 45 2O 25 20 25 90 1 No Cure.

The term wood resins, as employed in the present specification, denoteswood rosin and its various derivatives such as hydrogenated wood rosinand esterified wood rosin, examples of the latter being the polyhydricalcohol esters, e.g., ethylene glycol or glycerol esters.

The various aspects and modifications of the present invention will bemade more clearly apparent by reference to the following description andaccompanying examples.

Examples 1 through 5 As shown by the above data, the use of wood rosin,-

hydrogenated wood rosin, esterified wood rosin or benzoic acidaccelerates the cure rate of halogenated butyl rubber. Whereas neitherthe conventional zinc oxide nor sulfur cure gave a vulcanizate whencured for 20 minutes at 287 F., the compositions of the presentinvention give vulcanizates of good physical properties when cured underthese conditions.

The inability of succinic acid to accelerate the cure of halogenatedbutyl rubber is demonstrated in sam- Examples 6 i and 7 Halogenatedbutyl rubber A was compounded into the base recipe shown below, the typeof acid or anhydride incorporated in the recipe being as indicated inthe samples. The resulting compositions were then cured for varyingperiods of time at 287 F. and their 300% modulus to measure the extentof the tightness of the 75 cure.

TABLE 11 Base Recipe, Parts by Wt.:

Halogenated Butyl Rubber A 100 MT B c 60 Process Oil.

As illustrated in Table H, the incorporation of either maleic orsalicyclic acid (both known retarders) accelerates the cure rate ofhalogenated butyl rubber and gives a much more firmly cured recipe forshort cure periods. The inability of either fumaric acid or phthalicanhydride to accelerate the cure rate of halogenated butyl rubber isillustrated by samples (d) and (e).

Various modifications may be made to the present invention. Thecompositions of the present invention may be utilized for wire coatings,extruded or molded, items such as conveyor belting, tubes andparticularly tires and tire liners, chafers, sidewalls or tiegumsbetween butyl rubbers and more highly unsaturated rubbers.

Having described the present invention, that which is sought to beprotected is set forth in the following claim.

What is claimed is:

A process which consists essentially of the steps of (a) admixing, per100 parts of a rubbery halogenated copolymer of between about 85 andabout 99.5 wt. percent of a C to C isoolefin and between about 15 andabout 0.5 wt. percent of a C to C multiolefin, said halogenatedcopolymer containing 0.5-3 wt. percent combined halogen, (1) betweenabout 1 and about 20 wt. percent of zinc oxide and (2) between about 0.1and about 15 wt. percent of maleic anhydride, and (b) curing saidcornposition at a temperature of between about 200 F. and about 400 F.to provide a vulcanizate therefrom.

References Cited by the Examiner gredients, ed. II, Conway Printing Co.,N.Y., 1947, pages -136, 246 TS 1890153.

JOSEPH L. SCHOFER, Primary Examiner. E. I. SMITH, Assistant Examiner.

